Randomized Controlled Comparison of Valveless Trocar (AirSeal) vs Standard Insufflator with Ultralow Pneuomoperitoneum During Robotic Prostatectomy

Abstract

Objective:

To compare valveless insufflation (AirSeal^®) with a conventional insufflation system (CIS) during robotic prostatectomy (RP) and the ability to use ultralow pneumoperitoneum at 6 mm Hg with each system as well as comparison of physiologic outcomes and pain scores.

Patients and Methods:

We conducted a prospective study of 100 patients randomized to AirSeal or CIS during RP. The frequency of need for increasing pneumoperitoneum was assessed as well as arterial blood gases, respiratory/hemodynamic parameters, pain scores, and analgesic requirements. Quality of smoke evacuation and scope cleaning frequency were also measured.

Results:

All procedures were completed at 6 mm Hg without needing to increase pressures with either insufflator. There were no statistically significant differences in partial pressure of carbon dioxide (PaCO₂), partial pressure of oxygen (PaO₂), HCO₃, pH, carbon dioxide (CO₂) elimination, or end-tidal carbon dioxide pressure (EtCO₂) between groups. The AirSeal group had a lower maximum peritoneal pressure (7.9 vs 9.9 mm Hg, p < 0.001) but without differences in pain scores or analgesics. Surgeon-assessed smoke evacuation was poorer using CIS with more laparoscope cleanings in nonobese patients than with AirSeal (2.1 vs 3.0, p = 0.026).

Conclusion:

Valveless-trocar insufflation provided more stable pressure but without benefits in physiologic or pain parameters. Previously identified benefits may have been negated by being able to complete all procedures at ultralow pressure with either insufflator, although an expert bedside assistant moderating suction may have contributed to feasibility of maintaining low pressure with CIS. A randomized trial of 6 vs 15 mm Hg is currently underway. The ClinicalTrials.gov Identifier: NCT02114164.

Introduction

Gas insufflation of the abdominal cavity is a necessity in laparoscopic or robotic surgery to create an appropriate working space, but standard practices regarding pneumoperitoneum are based more upon routine and dogma than evidence. Carbon dioxide (CO₂) use is standard based upon its well-studied features (odorless, nonflammable, and rapidly cleared by systemic circulation), but little attention has been given to evaluating the optimum pressure and the impact of pressure stability.¹

Evidence suggests that elevated (sustained or spiking) intra-abdominal pressure (IAP) as well as sudden drops of pneumoperitoneum and recovery affect cardiovascular, respiratory, and renal function,^1

–4 but this has had little impact on pneumoperitoneum practices across specialties. Such physiologic consequences may also be increased in the steep Trendelenburg position used during robotic prostatectomy (RP).² In addition, overdistention of the abdominal cavity may have implications for postoperative patient morbidity and recovery. Several authors have investigated the relation between IAP during laparoscopy and postoperative pain,^5,6 and we previously identified less postoperative pain after RP performed at an ultralow insufflation pressure of 6 mm Hg as retrospectively compared with 15 mm Hg.⁷ The routine use of higher pressures (12–15 mm Hg) remains standard in most laparoscopic/robotic surgery and has not changed in decades.

Conventional insufflation systems (CISs) use common trocars with silicone valves or “trap doors” and a one-way insufflation pump that responds to changes in IAP. As a result, the abdominal cavity becomes a closed environment susceptible to IAP spikes from any external compression or contraction of abdominal wall muscles, and the resulting limited air circulation increases moisture and smoke affecting visibility.^2,8,9 Loss of insufflation may occur with passage of instruments, CO₂ leakage, or suctioning/smoke evacuation.^4,9

The AirSeal^® System (Conmed, Inc., Utica, NY) replaces “trap door” and silicon valve trocars with valve-free trocars and an insufflation system with continuous airflow, filtration, and CO₂ recirculation. This constant gas flow affords continuous smoke evacuation and immediate response to minimal changes in IAP without delay.^8,9 The lack of physical valves also allows instantaneous venting of any pressure spikes.^10,11

It remains unclear whether the level of IAP or its stability has clinically relevant implications that should motivate a widespread change in practice such that additional investigations are necessary. We, therefore, performed a randomized study comparing CIS with valveless insufflation (AirSeal^®) at intentionally low pneumoperitoneum pressures. The primary endpoint was to determine whether maintaining low IAP is feasible and whether the level and stability of IAP impacts physiologic parameters, CO₂ elimination, or patient recovery.

Patients and Methods

A prospective randomized study of patients with localized prostate cancer undergoing RP by a single surgeon (R.A.) was performed between March 2016 and February 2017 with IRB approval. After informed consent, patients were randomly selected for valveless insufflation vs CIS with the appropriate type of assistant port and insufflation device connected to it with the remaining four ports being 8 mm robotic trocars in both groups.

All procedures were begun at an ultralow pneumoperitoneum pressure of 6 mm Hg per routine,⁷ and frequency of need to increase the pressure >6 mm Hg to complete the procedure (e.g., caused by loss of space/visibility from suctioning, leak) as well as maximum pressures used and duration were measured. The quality of smoke evacuation was assessed by the surgeon on a 3-point rating scale, and the number of laparoscope cleanings required per case was also recorded.

A standard anesthesia regimen was followed to create a uniform population. Any necessary adjustments in ventilator settings by anesthesia based upon intraoperative patient respiratory status were recorded. Postoperatively, scheduled Ketorolac and acetaminophen on an as-needed basis were given for pain control with oral narcotics reserved for breakthrough pain. Ondansetron was given as needed for nausea. Postoperative pain was evaluated at baseline, postoperatively, once every 30 minutes for the first hour, before transfer to the floor, and every 8 hours, including at discharge, using an 11-point numerical rating scale.

Arterial blood gases were taken at baseline, 60 minutes after insufflation, and at the end of the procedure. Respiratory and hemodynamic parameters (systolic and diastolic blood pressure, peak airway pressure, positive end expiratory pressure, respiratory rate [RR], heart rate, tidal volume, and end-tidal CO₂) were collected from the mechanical ventilators used by anesthesia. CO₂ elimination was calculated at the same time points using end-tidal carbon dioxide pressure (EtCO₂), tidal volume, RR, barometric pressure (p _B = 760 mm Hg), partial pressure of water vapor (P_H2O = 13 mm Hg), and patient's weight (kg) based upon the equation described by Ng et al.¹²

For demographics and preoperative clinical characteristics, all categorical variables were described as percentages and continuous variables with means and standard deviations. Number of interventions required by the anesthesiologists were compared using Poisson regression. t-Tests or Wilcoxon rank sum tests were used for maximum peritoneal pressure and operative time (OT). Smoke evacuation quality was evaluated with chi-square test. For the evaluation of pain scores and morphine equivalent dose (MED) units, a linear mix model was applied. The difference in MED units between groups was analyzed using t-test. Statistical significance was set at p < 0.05. Power calculation to determine study size was based upon the primary endpoints of CO₂ elimination, EtCO₂, and partial pressure of oxygen (PaO₂) whereby the largest number of patients needed to detect a 25% difference with p < 0.05 and β = 0.1 was 94 patients.

Results

A total of 109 patients were enrolled with 9 patients withdrawing from the study for a total of 100 patients randomized to AirSeal vs CIS with 50 patients in each arm. No patient was excluded or withdrew after randomization. The overall mean age was 61.5 ± 6.2 years (range 47–75 years) and mean body mass index (BMI) 28.7 ± 3.8 kg/m² (range 21.5–40.7 kg/m²), without statistically significant differences between groups after randomization (p = 0.5 and p = 0.3, respectively) (Table 1).

Table 1.

Characteristics of Patients Randomized to Conventional vs Valveless Insufflation for Robotic Prostatectomy

	Overall	AirSeal^®	CIS	p
Mean age, years (SD, range)	61.5 (±6.2, 47–75)	61 (±5.6, 47–72)	62 (±6.7, 48–75)	0.44
Mean BMI, kg/m² (SD, range)	28.7 (±3.8, 21.5–40.7)	29.1 (±4.3, 22–39)	28.3 (±3.3, 21.5–40.7)	0.30
Race, n (%)
Caucasian	92 (92)	50/50 (100)	42/50 (84)	—
African American	7 (7)	—	7/50 (14)	—
Other	1 (1)	—	1/50 (2)	—
Nerve sparing, n (%)	69 (69)	35 (70)	34 (68)	0.98
Mean preoperative Hb, g/dL (SD, range)	14.8 (±1.0, 12.4–17.3)	15.1 (±1.0, 13–17.3)	14.7 (±1.0, 12.4–17.1)	0.083
Mean preoperative creatinine, mg/dL (SD, range)	0.92 (±0.1, 0.59–1.96)	0.89 (±0.1, 0.59–1.42)	0.96 (±0.2, 0.59–1.96)	0.06
Mean preoperative PSA, ng/mL (SD, range)	7.3 (±5.3, 1.5–38.5)	7.5 (±5.7,1.5–38.5)	7.2 (±4.89, 2.37–26.8)	0.777
ASA score, n (%)
2	68 (68)	35/50 (70)	33/50 (66)	0.83
3	32 (32)	15/50 (30)	17/50 (34)
Preoperative Gleason (SD, range)	6.7 (±0.7, 6–9)	6.8 (±0.73, 6–9)	6.6 (±0.74, 6–9)	0.282
Pathologic Gleason (SD, range)	7.0 (±0.6, 6–9)	6.9 (±0.58, 6–9)	7.1 (±0.73, 6–9)	0.231
Clinical stage
T1c	67 (67)	32 (64)	35 (70)
T2a-c	30 (30)	16 (32)	14 (28)
T3a-b	3 (3)	2 (4)	1 (2)
Pathologic stage				0.91
T2		27/50 (54)	29/50 (48)
T3a		20/50 (40)	18/50 (36)
T3b		3/50 (6)	3/50 (6)

ASA = American Society of Anesthesiology; BMI = body mass index; CIS = conventional insufflation system; PSA = prostate specific antigen; SD = standard deviation.

All procedures were able to be completed at IAP of 6 mm Hg without any need to increase pneumoperitoneum with either conventional or valveless insufflators. There were no significant differences in partial pressure of carbon dioxide (PaCO₂), PaO₂, HCO₃, pH, CO₂ elimination, and EtCO₂ between both groups at each time point (Table 2). Using a zero inflated Poisson regression model, no significant differences were found in the number of ventilator interventions required by anesthesia providers between groups (0.69 vs 0.66, p = 0.41). The CIS group had higher maximum peritoneal pressures (7.9 vs 9.9 mm Hg, p < 0.001). Spikes in IAP >8 mm Hg were less frequent in the AirSeal group (24% vs 68%, p = 0.0001).

Table 2.

Physiologic and Respiratory Parameters Measured During Robotic Prostatectomy Using Conventional vs Valveless Insufflation

Time point	AirSeal	CIS	p
Mean PaCO₂ mm Hg (SD, range)
Baseline	39.5 (4.9, 25.3–48.0)	39.2 (5.3, 32.1–45.9)	0.79
60 minutes	41.5 (7.7, 17.4–41.2)	41.2 (5.2, 28–51.7)	0.82
Procedure end	45.1 (6.1, 29.5–54.8)	44.1 (5.5, 32–55.1)	0.39
Mean PaO₂ mm Hg (SD, range)
Baseline	361.9 (79.3, 171–508)	364.3 (81.9, 107–505)	0.88
At 60 minutes	283.9 (115.4, 39.1–494)	294 (105.0, 100–473)	0.65
Procedure end	286.5 (99.1, 146–482)	290.2 (99.4, 115–468)	0.86
HCO₃ mean (SD, range)
Baseline	24.48 (2.01, 16.5–36.9)	24.57 (1.83, 21.4–28.5)	0.82
60 minutes	24.31 (2.16, 15.3–27.5)	24.22 (2.04, 17.8–29.4)	0.83
Procedure end	24.23 (2.11, 14.8–27.3)	24.32 (1.95, 18.9–28.8)	0.83
Mean pH (SD, range)
Baseline	7.40 (0.04, 7.3–7.49)	7.41 (0.04, 7.36–7,52)	0.43
60 minutes	7.37 (0.05, 7.28–7.45)	7.38 (0.05, 7.3–7.48)	0.40
Procedure end	7.34 (0.05, 7.23–7.45)	7.35 (0.05, 7.27–7.45)	0.15
Mean CO₂ elimination mm Hg (SD, range)
Baseline	3.15 (0.67, 2.0–5.0)	3.28 (0.64, 2.0–4.9)	0.42
60 minutes	3.24 (0.74, 2.0–5.2)	3.28 (0.6, 1.7–4.4)	0.75
Procedure end	3.04 (1.35, 0.6–5.3)	3.11 (0.65, 0.4–7.4)	0.99
Mean EtCO₂ mm Hg (SD, range)
Baseline	31.47 (3.9, 24–41)	29.96 (3.1, 19–50)	0.13
60 minutes	32.80 (3.6, 25–43)	30.96 (3.2, 24–39)	0.018^*
Procedure end	34.77 (8.9 15–46)	34.17 (7.2, 20–50)	0.712

Statistically significant.

There were no differences between the two cohorts in pain scores at the four time points (30, 60 minutes, upon transfer to floor, and before discharge). Using a liner mixed model built to adjust for the effect of group, time, and pain medication given measured in MEDs, the amount of pain medication given in postanesthesia care unit (PACU) and after leaving PACU was not significantly different between the groups. Three nausea and two vomiting events occurred in the CIS group, and one nausea and no vomiting events were reported in the AirSeal group (p = 0.32 and p = 0.16, respectively).

There was no statistically significant difference in OT between groups (153 vs 159 minutes, p = 0.192). Estimated blood loss was significantly lower in the CIS group compared with the AirSeal group but by only 20 mL on average (126.5 vs 146.5 mL, respectively; p = 0.031) with no difference in postoperative hemoglobin (15.1 vs 15.1 g/dL, p = 0.99). There were no significant differences in postoperative creatinine, time in PACU, and urine output between groups (0.96 vs 1.0 mg/dL, p = 0.3; 1.2 vs 1.3 hours, p = 0.683 and 1439 vs 1527 mL, p = 0.54, respectively). Sixty-four patients were discharged on the same day as surgery, including 30/50 (60%) in the AirSeal group and 34/50 (68%) in CIS group, with the rest discharged the next day for a mean length of stay of 0.4 vs 0.3 days, respectively (p = 0.41).

Given that ventilation can be affected by BMI particularly in Trendelenburg position, we assessed outcomes stratified by obese vs normal BMI. With all procedures performed at ultralow pressure of 6 mm Hg, the only differences identified were a lower mean arterial HCO₃ at 60 minutes (24.96 vs 23.86 mEq/L, p = 0.04) in patients with BMI >30 and less laparoscope cleanings favoring the AirSeal group with BMI <30 (2.1 vs 3.0, p = 0.026). Otherwise, no physiologic differences or need for ventilator adjustments were seen regardless of BMI.

Discussion

As in any other laparoscopic procedure, RP requires the creation of an adequate working space with an adequate and continuous pneumoperitoneum for visibility and safety.⁸ The ideal method to achieve this is uncertain with well-entrenched practices in terms of pressure settings and devices that are not based on strong evidence. Previous studies, including our own experience, had identified a potential benefit using lower than typical insufflation pressures.⁷ Hypothetically, a more stable pneumoperitoneum might also be expected to have potential improvements in respiratory physiology or clinical benefits in terms of postoperative pain and recovery.

We performed a randomized prospective study comparing AirSeal with CIS to investigate these concepts. All procedures were started at an ultralow pneumoperitoneum pressure of 6 mm Hg to allow determination for feasibility with either insufflation device or alternatively to measure how often the pressure setting was increased if needed to safely complete the operation. Since all 100 procedures were able to be completed at 6 mm Hg regardless of patient factors (e.g., BMI up to 40.7 kg/m²), feasibility of ultralow pneumoperitoneum during RP was demonstrated for both CIS and valveless insufflation but precluded identification of differences related to pressure settings.

Other studies of valveless insufflation for laparoscopic or robotic surgery have found favorable physiologic affects using AirSeal as compared with CIS, and some studies comparing standard vs lower pneumoperitoneum have found a benefit to lower pressures.^1,2,7,13 To our knowledge, our study is the first comparison of CIS vs valveless insufflation using low pressure in both arms. The lack of identified physiologic differences between groups leads us to consider that at ultralow pressures, any detectable differences in physiologic parameters between insufflation systems might be minimized or even disappear. In addition, the benefits that have been identified using low pressure AirSeal rather than standard pressure CIS, such as that seen by Sroussi et al. in their study of 7 mm Hg AirSeal vs 15 mm Hg CIS in gynecology,⁵ may be equally seen with low pressure CIS.

Even with the more stable pneumoperitoneum and less overall pressure spikes we observed in the valveless insufflation group, we still did not identify any significant differences in intraoperative PaO_2, PaCO₂, HCO₃, and pH at the three time points measured. Interventions for adjustment of ventilator settings by the anesthesia team were also similar in both groups. This suggests that spikes in pressure may be too transient to have a physiologic impact or it may be that any potential impact of such spikes is negated by operating at a low pressure to begin with. The average maximum pressure we observed with CIS (9.9 mm Hg), whereas higher than with AirSeal (7.9 mm Hg), was still lower than the typical pressure used continuously by most surgeons throughout their laparoscopic or robotic surgeries.

The benefit of valveless trocars in avoiding spikes is because any sudden pressure from abdominal wall contractions or external pushing on the abdomen are immediately dissipated by leak from the trocar as opposed to with CIS/valved trocars where there is no automatic venting because the abdomen is a closed system. If such spikes can potentially lead to more pain, particularly shoulder pain, from peritoneal or diaphragmatic stretch, this could explain why some groups have found less pain with valveless insufflation.⁶ Shahait et al. compared CIS with AirSeal during RP using 15 mm Hg in both groups and found lower pain scores at each of four time points with the valve-less system.¹⁰ We saw a similar trend, but the difference did not reach statistical significance.

We also found no difference in the amount of analgesics consumed in contrast with previous reports associating valveless insufflation with less need for pain medication.^10,13 Once again, it is possible that any such benefits of valveless insufflation are negated when an ultralow pressure is used in both groups. If pressure spikes are the cause of additional pain with CIS where there is no “pop-off” mechanism, then operating at ultralow pressures with CIS might compensate for this and prevent spikes from ever reaching a level that could cause undue stretch and pain. If this is the case, then a pain benefit with valveless insufflation over CIS would not be seen using ultralow pressures as we did.

Stability of pneumoperitoneum is important beyond spikes since loss of pressure is also an issue and can delay progress of the operation or can be a safety hazard. Previous studies have shown less pressure spikes as well as faster restoration after pressure loss when using valveless insufflation rather than CIS.^7
–9,11,13 Loss of pressure was not prohibitive to operating at 6 mm Hg with either insufflation device in our study but with a subjective experience that liberal suction does not affect pneumoperitoneum even at 6 mm Hg with AirSeal, whereas more judicious suctioning is needed to maintain a working space with CIS.

It is likely that having an expert bedside assistant in our procedures moderating suction contributed to maintaining pressure with CIS given that these devices do not maintain stability of pressures similar to the AirSeal system. Still, our study shows that RP can be performed at ultralow pressure even with CIS such that surgeons without access to advanced insufflation should not be dissuaded from using lower than their usual pneumoperitoneum pressures. Of course, less experienced RP surgeons may require more time to adjust to ultralow IAP. Nevertheless, we would advocate for such surgeons to consider progressive reduction of pneumoperitoneum pressure to the lowest level at which they are comfortable even if not as low as 6 mm Hg.

Our study also evaluated the effect of the insufflation system on surgeon visibility. Smoke evacuation quality was poorer on average in the CIS group. The constant gas cycling with AirSeal leads to less moisture and smoke accumulation as described by several other authors as well, which was a benefit preserved at ultralow pressure.^9,13,14 This likely also resulted in our finding that fewer scope cleanings were required in the AirSeal cohort, specifically in patients with BMI <30 in whom less intra-abdominal fat allows less scope cleanings in general in our experience.

Given the limitations of our study and implications for reaching conclusions about CIS vs valveless insufflation, we were not able to identify physiologic or postoperative recovery benefits but established the feasibility of performing RP at ultralow pneumoperitoneum with either insufflation method and more stability with AirSeal. To better elucidate the potential benefits of using ultralow pressure, we are currently performing a randomized controlled trial comparing ultralow pneumoperitoneum (6 mm Hg) with standard pneumoperitoneum (15 mm Hg).

Conclusion

Performing RP at an ultralow pneumoperitoneum pressure of 6 mm Hg is feasible with either CIS or valveless-trocar insufflation, although having an expert bedside assistant moderating suction may have contributed to maintaining low pressure with CIS. Valveless insufflation provided more stable IAP during RP, but no benefits in physiologic or pain parameters were identified. The stability of IAP afforded by the AirSeal system could be helpful for surgeons contemplating using lower pressure where small changes in pneumoperitoneum pressure can affect the working space and visibility. In addition, the AirSeal system may also improve visibility through better smoke evacuation and decrease interruptions for laparoscope cleaning.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

This study was supported by a grant from Surgiquest, Inc.

Abbreviations Used

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